Current-source inverters (CSIs) have been an attractive solution for high-power motor drives. Traditionally, CSIs have been implemented using thyristors, which are solid-state semiconductor devices with four layers of alternating N-type and P-type material that can act as bistable switches. A common challenge when designing circuits using thyristors is that typical thyristors are not fully controllable. In other words, after a typical thyristor is turned on by a gate signal, the thyristor remains on until a turn-off condition occurs. The turn-off condition may be the application of a reverse voltage to the terminals, or when the current through the thyristor falls below a threshold holding current.
A gate turn-off thyristor (GTO) is a special type of fully controllable high-power thyristor, which can be turned on or off by a gate signal. A GTO can be turned on by providing a positive current between the gate and cathode of the device, and likewise can be turned off by providing a negative current across the same terminals. As such, GTOs have been a popular choice for thyristor circuit applications such as CSIs.
However, current implementations of CSIs using GTOs suffer from drawbacks such as low-frequency torque pulsation, harmonic heating, and unstable operation at low speeds. Additional tuning for GTOs such as that of pulse width modulation present other issues such as insulation failure, bearing currents, common-mode voltages and over-voltages due to long cables.